Polylactic acid resin composition, method for producing polylactic acid resin composition, and polylactic acid resin molded article

ABSTRACT

A polylactic acid resin composition contains a polylactic acid resin having an epoxy group, and a flame-retardant additive.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2010-039383 filed Feb. 24, 2010.

BACKGROUND

(i) Technical Field

The present invention relates to a polylactic acid resin composition, amethod for producing a polylactic acid resin composition, and apolylactic acid resin molded article.

(ii) Related Art

Recently, from the standpoint of environmental conservation, resinmolded articles that use a biodegradable resin have been investigatedfor various applications. Among these applications, in the field ofhousings of electronic products or the like, flame retardancy isrequired for such resin molded articles.

SUMMARY

According to an aspect of the invention, there is provided a polylacticacid resin composition containing a polylactic acid resin having anepoxy group, and a flame-retardant additive.

DETAILED DESCRIPTION

An exemplary embodiment of the invention will now be described indetail. Note that the invention is not limited to the exemplaryembodiment described below and the invention can be carried out byvariously modifying within the scope of the gist of the invention.

Polylactic Acid Resin Composition

(A) Polylactic Acid Resin

In this exemplary embodiment, an example of a polylactic acid resinhaving a molecular terminal modified by a reaction with a monoepoxygroup-containing compound (i.e., monoepoxy compound), the polylacticacid resin being used as a component (A), is a polylactic acid resin inwhich an epoxy group has been introduced to a molecular terminal thereofby a reaction between a polylactic acid resin and a monoepoxygroup-containing compound (hereinafter also referred to as “epoxygroup-terminated polylactic acid resin”).

Examples of the polylactic acid resin used in this exemplary embodimentinclude polylactic acid, copolymers of polylactic acid and otheraliphatic polyesters, blends of polylactic acid and other aliphaticpolyesters, and alloys of polylactic acid and other aliphaticpolyesters. When the polylactic acid resin is composed of a copolymer, ablend, or an alloy, the amount of lactic acid component contained in thepolylactic acid resin is 50% by weight or more, preferably 60% by weightor more, and further preferably 70% by weight or more.

Among these, polylactic acid, and copolymers of polylactic acid andother aliphatic polyesters are preferable, and polylactic acid is morepreferable. The polylactic acid is not particularly limited so long asthe polylactic acid is a polymer in which a lactic acid unit isrepeated, and known polylactic acid may be used as the polylactic acid.The polylactic acid may contain, as a lactic acid component, L-lacticacid, D-lactic acid, or both L-lactic acid and D-lactic acid. From thestandpoint of flexibility, among the lactic acid components of thepolylactic acid, preferably, the content of L-lactic acid is 80% byweight or more or the content of D-lactic acid is 80% by weight or more.Furthermore, the polylactic acid may contain copolymer components otherthan lactic acid so long as advantages of the invention are notimpaired. Examples of the other copolymer components includehydroxybutyric acids, hydroxyvaleric acids, and citric acids.

A method for producing polylactic acid or a copolymer of polylactic acidand other aliphatic polyesters is not particularly limited, and hithertoknown methods may be employed. Examples of the method include (1) amethod in which dehydration polycondensation is directly conducted usinglactic acid or a mixture of lactic acid and an aliphatichydroxycarboxylic acid as a starting material (for example, U.S. Pat.No. 5,310,865); (2) a ring-opening polymerization method including meltpolymerization of a cyclic dimer of lactic acid (lactide) (for example,U.S. Pat. No. 2,758,987; (3) a ring-opening polymerization methodincluding melt polymerization of a cyclic dimer of lactic acid andaliphatic hydroxycarboxylic acid, e.g., lactide or glycolide, andε-caprolactone in the presence of a catalyst (for example, U.S. Pat. No.4,057,537); (4) a method in which dehydration polycondensation isdirectly conducted using a mixture of lactic acid, an aliphatic dihydricalcohol, and an aliphatic dibasic acid (for example, U.S. Pat. No.5,428,126); (5) a method including condensing polylactic acid and apolymer of an aliphatic dihydric alcohol and an aliphatic dibasic acidin the presence of an organic solvent (for example, EP0712880/A2); and(6) a method in which solid-phase polymerization is conducted in atleast one step in producing a polyester polymer by conducting adehydration polycondensation reaction of lactic acid in the presence ofa catalyst.

The polylactic acid resin used in this exemplary embodiment may be ablend or an alloy of polylactic acid and an aliphatic polyester, asrequired. Examples of the aliphatic polyester include polymers that canbe produced by various combinations of an aliphatic hydroxycarboxylicacid other than polylactic acid, an aliphatic dihydric alcohol, and analiphatic dibasic acid. As a method for producing the aliphaticpolyester, methods similar to the methods for producing polylactic acidor a copolymer of polylactic acid and other aliphatic polyesters mayalso be employed, but the method is not limited thereto.

Specific examples of the aliphatic hydroxycarboxylic acid other thanpolylactic acid include glycolic acid, 3-hydroxybutyric acid,4-hydroxybutyric acid, 3-hydroxyvaleric acid, 4-hydroxyvaleric acid, and6-hydroxycaproic acid. Furthermore, cyclic esters of an aliphatichydroxycarboxylic acid, such as glycolide, which is a dimer of glycolicacid, and ε-caprolactone, which is a cyclic ester of 6-hydroxycaproicacid may also be used. These may be used alone or in combination of twoor more types of compounds.

Specific examples of the aliphatic dihydric alcohol include ethyleneglycol, diethylene glycol, triethylene glycol, polyethylene glycol,propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol,3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentylglycol, polytetramethylene glycol, and 1,4-cyclohexanedimethanol. Thesemay be used alone or in combination of two or more types of aliphaticdihydric alcohols.

Specific examples of the aliphatic dibasic acid include succinic acid,oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, undecanedioic acid, anddodecanedioic acid. These may be used alone or in combination of two ormore types of aliphatic dibasic acids.

The average molecular weight of the polylactic acid resin used in thisexemplary embodiment is usually 10,000 or more and preferably 20,000 ormore, but is 200,000 or less and preferably 150,000 or less in terms ofweight-average molecular weight. If the average molecular weight of thepolylactic acid resin is excessively small, formation of a network bycross-linking tends to become insufficient. If the average molecularweight of the polylactic acid resin is excessively large, cross-linkingreactivity tends to decrease.

In this exemplary embodiment, a polylactic acid resin prepared by addinga crystallization accelerator to polylactic acid may be used. Examplesof the crystallization accelerator include inorganic fillers such astalc and glass fiber; mica; trimesic acid tricyclohexylamide; trimesicacid tris(2-methylcyclohexylamide); and trimesic acidtris(2,3-dimethylcyclohexylamide). The amount of crystallizationaccelerator added is usually in the range of 0.1 to 30 parts by weightrelative to 100 parts by weight of the polylactic acid resin.

(Monoepoxy Group-Containing Compound)

The monoepoxy group-containing compound (monoepoxy compound) is notparticularly limited so long as the compound has one epoxy group in itsmolecule. In consideration of reactivity with a molecular terminal ofthe polylactic acid resin, an epoxy compound having at least onehydroxyl group in its molecules is used as an example of the monoepoxygroup-containing compound in this exemplary embodiment.

Specific examples of such an epoxy compound include epoxy alcoholcompounds, glycidyl ether compounds of a polyhydric alcohol, and anaromatic ring-containing polyglycidyl ether compounds.

In this exemplary embodiment, among these epoxy compounds having atleast one hydroxyl group, epoxy alcohol compounds are preferable.Furthermore, a hydroxy-epoxy compound represented by general formula (1)below is more preferable.

In general formula (1), R represents a linear alkylene group, branchedalkylene group, arylene group, or arylalkylene group having 1 to 10carbon atoms.

Examples of the linear alkylene group represented by R in generalformula (1) include a methylene group, an ethylene group, a propylenegroup, a butylene group, a pentylene group, and a hexylene group.Examples of the branched alkylene group include a 2-methylbutylenegroup, a 2-methylpropylene group, and a 2-methylhexylene group. Examplesof the arylene group include a phenylene group and a naphthylene group.Examples of the arylalkylene group include a phenylmethylene group, aphenylethylene group, and a phenylpropylene group.

Specific compounds represented by general formula (1) include glycidol,1-hydroxyethyl ethylene oxide, 1-hydroxyhexyl ethylene oxide,1-hydroxy-2-methylbutyl ethylene oxide, 1-hydroxy-2-methylhexyl ethyleneoxide, and 1-hydroxyethyl-2-phenylpropyl ethylene oxide.

According to this exemplary embodiment, in the epoxy group-terminatedpolylactic acid resin used as the component (A), a ratio of the numberof molecular terminals to which an epoxy group has been introduced by areaction with the monoepoxy group-containing compound to the totalnumber of molecular terminals of the polylactic acid resin used(hereinafter referred to as “terminal-epoxy group modification ratio”)is preferably at least 30%. Furthermore, the terminal-epoxy groupmodification ratio is more preferably at least 50%, and particularlypreferably at least 70%. If the terminal-epoxy group modification ratiois excessively low, the mechanical strength of resin molded articlesdecreases and the flame retardancy tends to decrease.

The terminal-epoxy group modification ratio is determined by a reactiontitration measurement of unreacted terminals. Specifically, a sample isdissolved in chloroform and is then allowed to react with certainamounts of a monocarboxylic acid and an alcohol. Subsequently, theamounts of the monocarboxylic acid and alcohol remaining as reactionresidues are quantified.

(B) Flame-Retardant Compound

A flame-retardant compound (i.e., flame-retardant additive) used as acomponent (B) in this exemplary embodiment is not particularly limited,and hitherto known additives may be used. Examples of such aflame-retardant compound include phosphorus flame-retardant compounds,boric acid flame-retardant compounds, inorganic flame-retardantcompounds, nitrogen flame-retardant compounds, halogen flame-retardantcompounds, organic flame-retardant compounds, and colloidalflame-retardant compounds. These may be used alone or in combination oftwo or more types of flame-retardant compounds.

Examples of the phosphorus flame-retardant compounds include ammoniumphosphate, ammonium polyphosphate, aluminum polyphosphate, melaminepolyphosphate, melamine pyrophosphate, red phosphorus, phosphate esters,tris(chloroethyl)phosphate, tris(monochloropropyl)phosphate,tris(dichloropropyl)phosphate, triallyl phosphate,tris(3-hydroxypropyl)phosphate, tris(tribromophenyl)phosphate,tris-β-chloropropyl phosphate, tris(dibromophenyl)phosphate,tris(tribromoneopentyl)phosphate, tetrakis(2-chloroethyl)ethylenediphosphate, dimethyl methyl phosphate,tris(2-chloroethyl)orthophosphate, aromatic condensed phosphates,halogen-containing condensed organophosphates,ethylenebis[tris(2-cyanoethyl)]phosphonium bromide, β-chloroethyl acidphosphate, butyl pyrophosphate, butyl acid phosphate, butoxyethyl acidphosphate, 2-ethylhexyl acid phosphate, melamine phosphate,halogen-containing phosphonates, and phenylphosphonic acid.

Examples of the boric acid flame-retardant compounds include compoundscontaining boric acid, such as zinc borate hydrate, barium metaborate,and borax.

Examples of the inorganic flame-retardant compounds include metalsulfate compounds such as zinc sulfate, potassium bisulfate, aluminumsulfate, antimony sulfate, potassium sulfate, cobalt sulfate, sodiumbisulfate, iron sulfate, copper sulfate, sodium sulfate, nickel sulfate,barium sulfate, and magnesium sulfate; ammonium salt flame-retardantcompounds such as ammonium sulfate; iron oxide combustion catalysts suchas ferrocene; metal nitrate compounds such as copper nitrate;titanium-containing compounds such as titanium oxide; guanidinecompounds such as guanidine sulfamate; carbonate compounds such aspotassium carbonate; metal hydroxides such as aluminum hydroxide andmagnesium hydroxide; zirconium compounds; molybdenum compounds; tincompounds; and montmorillonite.

Examples of the nitrogen flame-retardant compounds include cyanuratecompounds having a triazine ring.

Examples of the halogen flame-retardant compounds include chlorinatedparaffin, perchlorocyclopentadecane, hexabromobenzene, decabromodiphenyloxide, bis(tribromophenoxy)ethane,ethylenebis(dibromonorbornanedicarboximide),ethylenebis(tetrabromophthalimide), dibromoethyl dibromocyclohexane,dibromoneopentyl glycol, 2,4,6-tribromophenol, tribromophenyl allylether, tetrabromobisphenol A derivatives, tetrabromobisphenol Sderivatives, tetradecabromo diphenoxybenzene,tris(2,3-dibromopropyl)isocyanurate,2,2-bis(4-hydroxy-3,5-dibromophenyl)propane,2,2-bis(4-hydroxyethoxy-3,5-dibromophenyl)propane, poly(pentabromobenzylacrylate), tribromostyrene, tribromophenyl maleimide, tribromoneopentylalcohol, tetrabromodipentaerythritol, pentabromobenzyl acrylate,pentabromophenol, pentabromotoluene, pentabromodiphenyl oxide,hexabromocyclododecane, hexabromodiphenyl ether, octabromophenol ether,octadibromodiphenyl ether, octabromodiphenyl oxide, dibromoneopentylglycol tetracarbonate, bis(tribromophenyl)fumaramide,N-methylhexabromodiphenylamine, bromostyrene, and diallyl chlorendate.

Examples of the organic flame-retardant compounds include silicone oil;silica compounds such as silicon dioxide, low-melting-point glass, andorganosiloxane; compounds containing bisphenol A; glycidyl compoundssuch as glycidyl ethers; polyhydric alcohols such as diethylene glycoland pentaerythritol; modified carbamides; chlorendic anhydride; andphthalic anhydride.

Examples of the colloidal flame-retardant compounds include colloids offlame-retardant compounds such as hydroxides, e.g., aluminum hydroxide,magnesium hydroxide, and calcium hydroxide; hydrates, e.g., calciumaluminate, gypsum dihydrate, zinc borate, barium metaborate, borax, andkaolin clay; nitric acid compounds, e.g., sodium nitrate; molybdenumcompounds; zirconium compounds; antimony compounds; dawsonite; andphlogopite.

Among these flame-retardant compounds, phosphorus flame-retardantcompounds are preferable. In particular, phosphoric acid flame-retardantcompounds such as ammonium polyphosphate, aluminum polyphosphate,melamine polyphosphate, and aromatic condensed phosphates arepreferable.

In this exemplary embodiment, the amount of flame-retardant compound,which is the component (B), incorporated in the epoxy group-terminatedpolylactic acid resin, which is the component (A), is not particularlylimited. Usually, 5 parts by weight or more, or about 5 parts by weightor more of the flame-retardant compound, which is the component (B), isadded to 100 parts by weight of the polylactic acid resin, which is thecomponent (A). Furthermore, the amount of component (B) incorporated ispreferably 5 parts by weight or more or about 5 parts by weight or more,and further preferably 10 parts by weight or more or about 10 parts byweight or more. However, the amount of component (B) incorporated isusually 40 parts by weight or less or about 40 parts by weight or less,preferably 30 parts by weight or less or about 30 parts by weight orless, and further preferably 20 parts by weight or less or about 20parts by weight or less. If the amount of component (B) is excessivelysmall, flame retardancy tends to be insufficient. If the amount ofcomponent (B) is excessively large, durability tends to decrease.

The polylactic acid resin composition of this exemplary embodiment maycontain, as a component (C), a polylactic acid resin having a molecularterminal modified by a reaction between the epoxy group-terminatedpolylactic acid resin, which is the component (A), and theflame-retardant compound, which is the component (B).

In the polylactic acid resin used as the component (C), a ratio of thenumber of molecular terminals to which a flame-retardant compound hasbeen introduced by a reaction with the flame-retardant compound to thetotal number of molecular terminals of the polylactic acid resin used(hereinafter referred to as “terminal-flame-retardant compoundmodification ratio”) is preferably at least 10%. Furthermore, theterminal-flame-retardant compound modification ratio is more preferablyat least 20%. If the terminal-flame-retardant compound modificationratio is excessively small, the mechanical strength of resin moldedarticles decreases, and a long-term maintained property of themechanical strength also tends to decrease.

The terminal-flame-retardant compound modification ratio is determinedby measuring an infrared (IR) spectrum and a two-dimensional nuclearmagnetic resonance (NMR) spectrum. Specifically, the intensities of apeak attributable to epoxy are compared between a sample and acomposition obtained before the incorporation of the component (C),wherein the intensity of the peak obtained by measuring the compositionobtained before the incorporation of the component (C) is assumed to be100.

(Hydrolysis Inhibitor)

The polylactic acid resin composition of this exemplary embodiment mayfurther contain, as a component (D), a hydrolysis inhibitor. Byincorporating the hydrolysis inhibitor, which is the component (D),hydrolysis of the polylactic acid resin is suppressed, and a decrease inthe mechanical strength of resin molded articles obtained from theresulting resin composition tends to be suppressed.

Examples of the hydrolysis inhibitor that can be used as the component(D) include, but are not particularly limited to, compounds known asadditives that suppress hydrolysis of polymer compounds having acarboxyl group (—COOH), a hydroxyl group (—OH), or the like. Examples ofsuch compounds include carbodiimide compounds and oxazoline compounds.

Examples of the carbodiimide compounds include dicyclohexylcarbodiimide,diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide,dioctylcarbodiimide, diphenylcarbodiimide, and naphthylcarbodiimide.

Examples of the oxazoline compounds include2,2′-o-phenylenebis(2-oxazoline), 2,2′-m-phenylenebis(2-oxazoline),2,2′-p-phenylenebis(2-oxazoline),2,2′-p-phenylenebis(4-methyl-2-oxazoline),2,2′-m-phenylenebis(4-methyl-2-oxazoline),2,2′-p-phenylenebis(4,4′-dimethyl-2-oxazoline),2,2′-m-phenylenebis(4,4′-dimethyl-2-oxazoline),2,2′-ethylenebis(2-oxazoline), 2,2′-tetramethylenebis(2-oxazoline),2,2′-hexamethylenebis(2-oxazoline), 2,2′-octamethylenebis(2-oxazoline),2,2′-ethylenebis(4-methyl-2-oxazoline), and2,2′-diphenylenebis(2-oxazoline). These may be used alone or incombination of two or more types of hydrolysis inhibitors.

The amount of hydrolysis inhibitor added as the component (D) is notparticularly limited. In this exemplary embodiment, the amount ofhydrolysis inhibitor used as the component (D) is usually 5 parts byweight or less or about 5 parts by weight or less, and preferably 2parts by weight or less or about 2 parts by weight or less relative to100 parts by weight of the polylactic acid resin.

If the amount of hydrolysis inhibitor serving as the component (D)relative to the amount of polylactic acid resin is excessively large,gelation may occur and thus the moldability tends to decrease. From thestandpoint of flame retardancy, the ratio of the hydrolysis inhibitor tothe flame-retardant compound is preferably 1:2 to 1:50, or about 1:2 to1:50.

(Other Additives)

The polylactic acid resin composition of this exemplary embodiment maycontain known other additives. Examples of such known additives includea reinforcing material, inorganic filler, organic filler, anantioxidant, a heat stabilizer, an ultraviolet absorber, a lubricant,wax, and a coloring agent. These additives may be used alone or incombination of two or more.

Examples of the reinforcing material include glass microbeads, carbonfiber, chalk, quartz, asbestos, feldspar, mica, talc, wollastonite, andkaolin. Examples of the inorganic filler include alumina, silica,magnesia, ferrite, barium sulfate, calcium carbonate, and fullerene,besides carbon and silicon dioxide. Examples of the organic fillerinclude epoxy resins, melamine resins, urea resins, acrylic resins,phenolic resins, polyimide resins, polyamide resins, polyester resins,and fluorocarbon resins. These may be used alone or as a mixture of twoor more types of additives.

Examples of the antioxidant include phenolic, amine, phosphorus, sulfur,hydroquinone, and quinoline antioxidants.

Examples of the heat stabilizer include nitrogen-containing compoundssuch as basic nitrogen-containing compounds, e.g., polyamides,poly-β-alanine copolymers, polyacrylamide, polyurethanes, melamine,cyanoguanidine, and melamine-formaldehyde condensation products; andalkali metal- or alkaline earth metal-containing compounds such asorganic carboxylic acid metal salts (e.g., calcium stearate and calcium12-hydroxystearate), metal oxides (e.g., magnesium oxide, calcium oxide,and aluminum oxide), metal hydroxides (e.g., magnesium hydroxide,calcium hydroxide, and aluminum hydroxide), and metal carbonates;zeolite; and hydrotalcite.

Examples of the ultraviolet absorber include benzophenone,benzotriazole, cyanoacrylate, salicylate, and oxalic anilide ultravioletabsorbers.

Examples of the lubricant include petroleum lubricating oil such asliquid paraffin; synthetic lubricating oil such as halogenatedhydrocarbons, diester oil, silicone oil, and fluorine silicone; variousmodified silicone oil (e.g., epoxy-modified, amino-modified,alkyl-modified, or polyether-modified silicone oil); siliconelubricating substances such as copolymers of a silicone and an organiccompound, e.g., a polyoxyalkylene glycol; silicone copolymers; variousfluorine surfactants such as fluoroalkyl compounds; fluorine lubricatingsubstances such as trifluoromethylene chloride low polymers; wax such asparaffin wax and polyethylene wax; higher aliphatic alcohols; higheraliphatic amides; higher fatty acid esters; higher fatty acid salts; andmolybdenum disulfide.

Examples of the wax include olefin wax such as polypropylene wax andpolyethylene wax, paraffin wax, Fischer-Tropsch wax, microcrystallinewax, montan wax, fatty acid amide wax, higher aliphatic alcohol wax,higher fatty acid wax, fatty acid ester wax, carnauba wax, and rice wax.

Examples of the coloring agent include inorganic pigments, organicpigments, and dyes.

Method for Producing Polylactic Acid Resin Composition

An example of a method for producing a polylactic acid resin compositionof this exemplary embodiment is a method including melt-kneading apolylactic acid resin, a monoepoxy group-containing compound, aflame-retardant compound, and other optional components with a knownkneader. Examples of the kneader include a Banbury mixer, a single-screwextruder, a twin-screw extruder, a ko-kneader, a multi-screw extruder.Among these kneaders, a twin-screw extruder or a single-screw extruderis preferable.

Specifically, a polylactic acid resin, a monoepoxy group-containingcompound, a flame-retardant compound, and other optional components aremelt-kneaded with an extruder, preferably a twin-screw extruder at apreset cylinder temperature in the range of, for example, about 160° C.to 250° C., and preferably about 170° C. to 200° C., the resultingmixture is extruded, the resulting strands are cut to prepare apolylactic acid resin composition as a master batch in the form ofcolumnar pellets. Alternatively, the polylactic acid resin compositionmay be prepared as spherical pellets by a hot-cut method or anunder-water cut method without taking up the strands.

In this exemplary embodiment, by melt-kneading the polylactic acidresin, the monoepoxy group-containing compound, the flame-retardantcompound, and other optional components, an epoxy group is introduced toa molecular terminal of the polylactic acid resin to obtain the epoxygroup-terminated polylactic acid resin, which is the component (A).Furthermore, some of the epoxy groups that have been introduced tomolecular terminals of the epoxy group-terminated polylactic acid resinreact with the flame-retardant compound, which serves as the component(B), to obtain the polylactic acid resin in which the flame-retardantcompound has been introduced to a molecular terminal thereof, thepolylactic acid resin serving as the component (C).

In this exemplary embodiment, the amount of monoepoxy group-containingcompound added in order to obtain the epoxy group-terminated polylacticacid resin, which is the component (A), is not particularly limited. Theamount of monoepoxy group-containing compound is 1 part by weight ormore, or about 1 part by weight or more, and more preferably 2 parts byweight or more, or about 2 parts by weight or more relative to 100 partsby weight of the polylactic acid resin. However, the amount of monoepoxygroup-containing compound is 10 parts by weight or less, or about 10parts by weight or less, and more preferably 8 parts by weight or less,or about 8 parts by weight or less. If the amount of monoepoxygroup-containing compound relative to the amount of polylactic acidresin is excessively small, the terminal-epoxy group modification ratioof the polylactic acid resin decreases, and the mechanical strength ofresin molded articles tends to decrease.

The amount of flame-retardant compound added in order to obtain thepolylactic acid resin in which the flame-retardant compound has beenintroduced to a molecular terminal thereof, the polylactic acid resinfunctioning as the component (C), is not particularly limited. Theamount of flame-retardant compound is usually 5 parts by weight or more,or about 5 parts by weight or more, preferably 10 parts by weight ormore, or about 10 parts by weight or more relative to 100 parts byweight of the polylactic acid resin. However, the amount offlame-retardant compound is usually 40 parts by weight or less, or about40 parts by weight or less, preferably 30 parts by weight or less, orabout 30 parts by weight or less. If the amount of flame-retardantcompound relative to the polylactic acid resin is excessively small, theterminal-flame-retardant compound modification ratio of the polylacticacid resin decreases, and the mechanical strength of resin moldedarticles tends to decrease.

Polylactic Acid Resin Molded Article

A polylactic acid resin molded article is obtained by using thepolylactic acid resin composition described above. A polylactic acidresin composition molded article (hereinafter, simply referred to as“molded article”) of this exemplary embodiment contains a polylacticacid resin having a molecular terminal to which an epoxy group has beenintroduced, the polylactic acid resin serving as the component (A), anda flame-retardant compound serving as the component (B) in thepolylactic acid resin composition described above.

Furthermore, the molded article may contain, as a component (C), apolylactic acid resin having a molecular terminal modified by a reactionbetween the epoxy group that has been introduced to the terminal of thepolylactic acid resin serving as the component (A) and theflame-retardant compound serving as the component (B).

The molded article of this exemplary embodiment can be suitably used inapplications such as electronic/electric devices, household electricappliances, containers, and interior materials for automobiles. Morespecifically, the molded article can be suitably used in housings,various components, and the like of household electric appliances orelectronic/electric devices, wrapping films, cases for CD-ROMs or DVDs,tableware, food trays, drink bottles, and wrapping materials forchemicals. Among these, the molded article of this exemplary embodimentis suitable for components of electronic/electric devices.

Method for Producing Polylactic Acid Resin Molded Article

Examples of a method for producing a polylactic acid resin moldedarticle of this exemplary embodiment include known forming methods andare not particularly limited. Examples of the known forming methodsinclude film forming, extrusion molding, and injection molding. Amongthese methods, injection molding is preferable. Specifically, extrusionmolding can be conduced in accordance with commonly used method using aknown extruder such as a single-screw extruder, a multi-screw extruder,or a tandem extruder. Injection molding can be conduced in accordancewith a commonly used method using a known injection molding machine suchas an in-line screw-type injection molding machine, a multilayerinjection molding machine, or a double-head injection molding machine.

In this exemplary embodiment, the polylactic acid resin composition ispreferably injected into a mold at a cylinder temperature of aninjection molding machine in the range of 160° C. to 220° C. Thetemperature of the mold during injection molding is preferably in therange of 30° C. to 150° C.

A molded article of this exemplary embodiment has an improved mechanicalstrength, and the mechanical strength is maintained for a long period oftime (long-term maintained property), thus extending the lifecycle ofthe resulting product.

The reason why the mechanical strength of the molded article describedabove is improved is not clear, but is believed to be as follows.

When an epoxy group is introduced to a molecular terminal of apolylactic acid resin, the compatibility between the polylactic acidresin and a flame-retardant compound improves. Furthermore, theflame-retardant compound is introduced to some of molecular terminals towhich the epoxy groups have been introduced. Consequently, ahigher-order structure of the polylactic acid resin, which is disorderedby the incorporation of a flame-retardant compound in the related art,is maintained. Therefore, the mechanical strength of molded articles isimproved.

In addition, a water-absorbing property of the polylactic acid resinwhose molecular terminals are blocked decreases, and thus hydrolysisresistance is improved. Accordingly, it is believed that the mechanicalstrength of molded articles is maintained for a long period of time.

EXAMPLES

The invention will now be described in more detail by way of Examples.However, the invention is not limited to Examples below.

Examples 1 to 13 and Comparative Examples 1 to 4

A polylactic acid resin, a monoepoxy group-containing compound, and aflame-retardant compound were kneaded with a twin-screw extruder(produced by Toshiba Machine Co., Ltd., TEM58SS) under the conditions ofthe compositions and the cylinder temperature shown in Tables 1 and 2 toprepare pellets of a polylactic acid resin composition (Examples 1 to13). For comparison, pellets of resin compositions (Comparative Examples1 to 4) that contained no monoepoxy group-containing compound wereprepared under the conditions of the compositions and the cylindertemperature shown in Table 2.

Next, ISO multi-purpose dumbbell test specimens (thickness: 4 mm, width:10 mm, in accordance with the ISO527 tensile test and the ISO178 bendingtest) were molded using the pellets of the polylactic acid resincompositions described above. Characteristic tests of the polylacticacid resin molded articles were conducted as described below (Examples 1to 13). In addition, test specimens were similarly molded using theresin compositions of Comparative Examples 1 to 4, and thecharacteristic tests of each of the resin molded articles wereconducted. The results are shown in Tables 1 and 2.

(1) Terminal Modification Ratio of Polylactic Acid Resin

A ratio of the number of molecular terminals to which an epoxy group hasbeen introduced by a reaction with a monoepoxy group-containing compoundto the total number of molecular terminals of a polylactic acid resin(“terminal-epoxy group modification ratio (unit: %)) was determined by areaction titration.

A ratio of the number of molecular terminals to which a flame-retardantcompound has been introduced by a reaction with the flame-retardantcompound to the total number of molecular terminals of a polylactic acidresin (terminal-flame-retardant compound modification ratio (unit: %))was determined by IR and two-dimensional NMR spectroscopy.

(2) Flame Retardant Test of Polylactic Acid Resin Molded Article

Test specimens of the UL (Underwriters Laboratories, Inc.,) standardhaving two thicknesses (0.8 mm and 1.6 mm) were formed by injectionmolding with an injection molding machine (produced by Nissei PlasticIndustrial Co., Ltd., NEX50) using each of the polylactic acid resincompositions under the conditions of the cylinder temperatures shown inTables 1 and 2 and a molding cycle of 1 minute. A 20-mm vertical burningtest of the UL standard 94 was then conducted. As for the UL rating,“V0” means V-0 acceptance, “V1” means V-1 acceptance, and “NotV” meansnon-acceptance.

In the test, each of V-0 and V-1 is determined using five testspecimens. Specifically, a burner flame is applied to the lower edge ofa vertically supported strip specimen. This state is maintained for 10seconds, and the burner flame is then removed from the specimen. If theflame goes out, the burner flame is immediately reapplied for additional10 seconds and is then removed.

The rating V0 or V1 is determined on the basis of a flaming combustiontime after each of the first flame application and the second flameapplication, the total of the flaming combustion time and a glowingcombustion time after the second flame application, the total flamingcombustion time of the five specimens, and the presence or absence offlaming particles (drips).

When flaming combustion ceases within 10 seconds after each of the firstflame application and the second flame application, the specimens areevaluated as V-0. When flaming combustion ceases within 30 seconds aftereach of the first flame application and the second flame application,the specimens are evaluated as V-1. Furthermore, when the total of theflaming combustion time and the glowing combustion time after the secondflame application is within 30 seconds, the specimens are evaluated asV-0. When the total of the flaming combustion time and the glowingcombustion time after the second flame application is within 60 seconds,the specimens are evaluated as V-1.

Furthermore, when the total flaming combustion time of the fivespecimens is within 50 seconds, the specimens are evaluated as V-0. Whenthe total flaming combustion time of the five specimens is within 250seconds, the specimens are evaluated as V-1. Furthermore, it isnecessary that all the specimens do not burn out.

(3) Impact Strength of Polylactic Acid Resin Molded Article

ISO multi-purpose dumbbell test specimens (thickness of testing portion:4 mm, width: 10 mm) in accordance with the ISO527 tensile test and theISO178 bending test were formed as polylactic acid resin molded articlesusing the pellets of each of the polylactic acid resin compositions byinjection molding with an injection molding machine (produced by NisseiPlastic Industrial Co., Ltd., NEX50) under the conditions of thecylinder temperatures and the mold temperatures shown in Tables 1 and 2.

Next, the molded ISO multi-purpose dumbbell test specimens wereprocessed into Charpy test specimens with notches in accordance withISO179. A Charpy impact strength test was conducted to measure theCharpy impact strength of the polylactic acid resin molded articles(unit: kJ/m²).

Furthermore, the ISO dumbbell test specimens were left to stand in anenvironment of 55° C./85% for 1,000 hours. The ISO dumbbell testspecimens were processed into Charpy test specimens to measure theCharpy impact strength (long-term maintained property) (unit: kJ/m²).

TABLE 1 Examples 1 2 3 4 5 6 7 8 9 Resin Polylactic Terramac 100 100 100100 100 100 100 100 100 compositions acid resin TE-2000 ( *) Terramac —— — — — — — — — TE-7000 Monoepoxy 1-Hydroxyethyl ethylene 2 4 6 8 — — 44 4 group- oxide containing 1-Hydroxyhexyl — — — — 4 — — — — compoundethylene oxide 1-Hydroxy-2- — — — — — 4 — — — phenylpropyl ethyleneoxide Flame- Exolit OP 930 20 20 20 20 20 20 15 30 — retardant Exolit AP422 — — — — — — — — 20 compound PX 200 — — — — — — — — — (**) MPP-A — —— — — — — — — Hydrolysis Carbodiimide (***) — — — — — — — — — inhibitorKneading Cylinder temperature ° C. 170 180 180 180 180 180 180 190 170condition Terminal-epoxy group modification 53 75 83 89 78 73 75 74 75ratio (%) Terminal-flame-retardant compound 18 22 22 23 19 18 11 35 17modification ratio (%) Resin Molding Cylinder temperature ° C. 180 180180 180 180 180 180 180 170 molded condition Mold temperature ° C. 40 4040 40 40 40 40 40 40 articles Charpy After molding 5 6.5 6.8 6.5 6.2 6.15.9 6.3 6.1 impact After 55° C./85%/1000 3.8 4.8 5.2 5.5 5.8 5.1 5.1 5.95.2 strength hrs (kJ/m²) Flame 0.8 mm-V V1 V0 V0 V0 V0 V0 V0 V1 V0retardant 1.6 mm-V V0 V0 V0 V0 V0 V1 V0 V0 V1 test

TABLE 2 Comparative Examples Examples 10 11 12 13 1 2 3 4 ResinPolylactic Terramac 100 100 100 100 100 100 100 — compositions acidresin TE-2000 (*) Terramac — — — — — — — 100 TE-7000 Monoepoxy1-Hydroxyethyl 4 4 4 4 — — — — group- ethylene oxide containing1-Hydroxyhexyl — — — — — — — — compound ethylene oxide 1-Hydroxy-2- — —— — — — — — phenylpropyl ethylene oxide Flame- Exolit OP 930 — — 20 2020 40 10 20 retardant Exolit AP 422 — — — — — — — — compound PX 200 20 —— — — — — — (**) MPP-A — 20 — — — — — — Hydrolysis Carbodiimide (***) —— 2 — 2 2 3 3 inhibitor Kneading Cylinder 190 180 190 180 180 180 180180 condition temperature ° C. Terminal-epoxy group modification 74 7473 75 — — — — ratio (%) Terminal-flame-retardant compound 19 18 17 18 —— — — modification ratio (%) Resin Molding Cylinder 190 180 180 180 180180 180 180 molded condition temperature ° C. articles Mold temperature° C. 40 40 40 110 40 40 40 40 Charpy After molding 6.3 6.2 7.5 6.9 1.72.2 1.5 2.5 impact After 5.3 5.5 6.2 6.2 0.3 0.5 0.2 0.5 strength 55°C./85%/1000 hrs (kJ/m²) Flame 0.8 mm-V V0 V0 V0 V0 NotV NotV NotV NotVretardant 1.6 mm-V V0 V0 V0 V0 V1 V0 V1 V1 test

Note that the components of the polylactic acid resin compositions shownin Tables 1 and 2 are as follows:

-   (*) Polylactic acid resin-   Terramac TE-2000 (produced by UNITIKA Ltd.)-   Terramac TE-7000 (produced by UNITIKA Ltd.)-   (**) Flame-retardant compound-   Exolit OP 930: Aluminum polyphosphate (produced by Clariant (Japan)    K.K.)-   Exolit AP 422: Ammonium polyphosphate (produced by Clariant (Japan)    K.K.)-   PX 200: Aromatic condensed phosphate (produced by Daihachi Chemical    Industry Co., Ltd.)-   MPP-A: Melamine polyphosphate (produced by Sanwa Chemical Co., Ltd.)-   (***) Hydrolysis inhibitor: Carbodilite LA1 (produced by Nisshinbo    Chemical Inc.)

Referring to Tables 1 and 2, polylactic acid resin molded articlesobtained from polylactic acid resin compositions containing an epoxygroup-terminated polylactic acid resin used as the component (A) and aflame-retardant compound used as the component (B) showed satisfactoryresults for the flame retardant test and had high Charpy impact strength(kJ/m²). These results showed that good flame retardancy could berealized without impairing the mechanical strength of the polylacticacid resins (Examples 1 to 13).

In contrast, even when a flame-retardant compound was added topolylactic acid resins that did not have molecular terminals modified bya reaction with a monoepoxy group-containing compound in an amountsubstantially the same as that in Examples (Comparative Examples 1 to4), the Charpy impact strength (kJ/m²) decreased and satisfactory flameretardancy could not be obtained.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

1. A method for producing a polylactic acid resin compositioncomprising: kneading a polylactic acid resin, a flame-retardantadditive, and a hydroxy-epoxy compound represented by general formula(1):

wherein R represents a linear alkylene group, branched alkylene group,arylene group, or arylalkylene group having 1 to 10 carbon atoms.
 2. Themethod according to claim 1, wherein the amount of the hydroxy-epoxycompound is about 1 part by weight or more and about 10 parts by weightor less relative to 100 parts by weight of the polylactic acid resin. 3.The method according to claim 1, wherein the amount of theflame-retardant additive is about 2 parts by weight or more and about300 parts by weight or less relative to 100 parts by weight of thepolylactic acid resin.
 4. The method according to claim 1, wherein theamount of the flame-retardant additive is about 10 parts by weight ormore and about 200 parts by weight or less relative to 100 parts byweight of the polylactic acid resin.